Finding a political solution is challenging while the Trump administration is weighing its approach to the war

GENEVA—Peace talks between Syria’s regime and opposition face a formidable obstacle: Until President Donald Trump’s administration decides how to approach the six-year war, it makes little sense for anyone to compromise.

“It’s very difficult to reach any political solution if there is not a positive, active and serious role of the U.S.A.,” said Nasr Alhariri, head of the opposition delegation to the current round of talks now under way in Geneva.